Reports of advances in the creation of therapeutic agents for cancer treatment have increased in recent years. Nevertheless, the ability to localize chemotherapy agents at the tumor sites has been hindered by adverse toxicity to the normal tissue. The challenges of enforcing residence of the drug carriers at the tumor site have not been efficiently met by the existing technology. Additionally, the inability to control the release of drugs while at the tumor site is a major reason for the lack of efficiency of existing targeted drug delivery systems.
Heating organs and tissues as a treatment of cancer is well known. The first reference to link heat and the destruction of cancerous growths was as early as 3000 BC in the contents of an Egyptian papyrus and later in the writings of Hippocrates. More scientifically, the connection between disappearance of tumors and high fever, either from infections or artificially induced by bacterial toxins, have initiated a concept of thermotherapy. Reports on enhanced selective thermal sensitivity of animal tumors compared with normal tissue confirm that hyperthermia may be considered as a cytotoxic agent. There has been work conducted on many aspects of heat application to tumors, which has lead to rapid development in therapeutic applicator design and to the increased sophistication of hyperthermia equipment.
Hyperthermic temperatures increase blood circulation in tumors. The increase in temperature increases the presence of oxygen-bearing blood in tumor tissues, which is critical for increasing the effectiveness of ionizing radiation. Ionizing radiation, also referred to as radiotherapy, destroys tumor cells substantially through the formation of oxygen radicals that attack the cell DNA of a tumor. Oxygen-starved cells are three-times more resistant to ionizing radiation than are normal cells. Low oxygen levels in human tumors, referred to as hypoxia, have been linked to failure in achieving local tumor control through ionizing radiation. In addition, the degree of oxygen deficiency in cancerous tumors is a key predictor of the efficacy of ionizing radiation therapy. Results from molecular biology research demonstrate that hyperthermia treatments may be used in many different tumors particularly for local tumor control. Such hyperthermia treatments resulted in an increase in the survival rate of the patients, especially when hyperthermia was combined with radiation therapy.